Blue Star Lubrication

[Steve.S]

I wonder if any of you experts out there can help me with an explanation of the Blue Star lubrication system?
I see there is a pressure relief valve, which BSA call an oil feed ball valve, mounted horizontally in the timing cover.
It also has an oil pump bypass plunger and spring in the oil pump.
I assume that the ball valve operates in the same way as a normal Pressure Relief Valve, in that when the oil is cold and thick, the pressure is higher, and so pushes the ball valve off it's seat, allowing some of the oil to bleed off, thus reducing the pressure. However, I can't work out where this oil goes to. It doesn't go back into the sump, as there is no cross drilling. If it is directed into the timing case, this would just fill up with oil.
Also, can anyone confirm that the Bypass plunger in the oil pump is there to prevent excessive pressure and possible damage to the pump, in the event of a blockage, by recirculating the oil within the pump?
Can anyone confirm my thoughts, and does anyone know where the oil from the relief valve goes?

[Bicycle repair man]

It's not a pressure relief valve. It's actually a one way valve to prevent oil from the oil reservoir from siphoning into the crank chamber when the engine is stationary.  Early ones were set at 5psi and later ones at 10. The latter one had 10 stamped into the soft solder caulking at the end. BSA recommended that the later ones be fitted to enable a better reading at the oil gauge.
If you remove the valve and look at the cover, you will see a small drilling near the top. This is to divert oil that leaks through the thread back into the timing chamber.

[David Samways]

I too have puzzled over the lubrication system. In particular I have wondered about the setting of the manual valve on the timing chest. The 1930-36 Instruction Book (available in the club library) notes that it should be open between half and one turn, but I find the sentence that follows regarding the arbitraryness of this setting and the owner determining the "most economical setting consistent with adequate lubrication" somewhat alarming - especially after having spent over a grand on reconditioning the crank!

[Steve.S]

BRM, Thank you for your very helpful reply. I think I am now beginning to understand the system.
Steve.

[Steve.S]

David, Thanks to BRM, I have now looked in the Bruce Main Smith green book, where there is a drawing of the Pressure valve. It seems to me that there were many variations of the oiling system, so you have to be careful that you are reading the section that refers to your own engine.
The Book of the BSA by F.J. Camm mentions an automatic release valve (the plunger and spring in the oil pump). He says this regulates the oil pressure in accordance with the control valve setting.
I have read the BSA instructions many times, trying too understand it, and I now think that the advice is very accurate.
I think the 2 important points are the amount of smoke, just a whisper, and the oil pressure reading.
My problem is lots of smoke, and about 5lbs pressure. So I have progressively turned down the oil until just a whisper of smoke, which I am sure means the engine is receiving the correct amount of oil. The problem with this is that when hot at tickover the gauge shows 0lbs. It goes up to 4lbs when revving.
My view is that the engine doesn't  actually need any pressure at tickover, as there will be plenty of oil in the crankcase to stop it from seizing. But I would like to a see a little more pressure on the gauge. Rings are new and have done 1,000 miles, so I don't think that's the problem.
Now I know what the Oil Control Valve does, I may try increasing the spring pressure slightly, which should increase the gauge reading??  But will it also increase the amount of oil going into the engine?

[Bicycle repair man]

I had a similar low pressure reading. I rigged up a simple pressure tester using the air regulator from my air brush to test the pressure valve. It was leaking badly. I machine as much of the sealing solder away as possible until it revealed the screw head of the regulator cap. With a bit of heat I managed to remove the cap to inspect the ball and seat which were worn. I rebuilt the valve with a new ball which I reseated. I adjusted the valve to 10psi with my tester and resealed with solder. The result is 10 psi oil pressure cold at idle and 3-4psi hot. I run my oil supply adjuster at about one turn out.

[Steve.S]

Excellent advice. I think this may be my problem. I will try what you suggest. Sounds like you've got it spot on.

[Steve.S]

Jean Luc's post has reminded me that I haven't posted an update.
I took BRM's advice and removed the valve. I made up a regulator and pressure gauge, and found the valve wasn't sealing at all.
The lead seal wasn't marked with 5 or 10, but it did have the Piled Arms stamp with the letter B (1934). Great shame, but I had to melt it to gain access.
I removed the screw, spring and ball, which was a bit rusty. I renewed the ball, but it still wouldn't hold any pressure. I could see that the area around the seating was raised up, so I tried to ease it down as best I could, but it wasn't very successful. Maybe you could you a small end mill bit?
So, although the valve body is steel, all I could do was tap the ball into the seating. It took about 3 or 4 tries, but eventually it sealed. I adjusted it to 7lbs and soldered the end up.
When I started the bike, I had no oil pressure, so I removed the brass adjuster toggle and unscrewed the oil regulator screw, and the oil pressure increased, so I set it to about 8lbs at half a turn out.
I now have a steadyish oil pressure of about 7 to 8lbs, hot or cold and on tickover (which seems a little odd, but I'm not complaining).
So thank you BRM. I would never have got there by myself.